Nanoscale domain structures and polarization reversal behaviour in (111)-oriented PZT60/40 thin film were investigated in-situ with scanning force microscopy p iezoresponse mode. Complex domain contrast is related to the arrangement of doma ins in grains and to the orientation of the grains in the film. The step structu re of ～ 30 nm in width was directly observed, which was formed during the polar ization reversal process. The presence of the step structures reveals that the f orward domain growth mechanism prevails in the polarization switching process of PZT60/40 thin films.